1. Field of Invention
This invention relates generally to an anchor and stress plate assembly for securing an insulation layer to the deck of a roof, and more particularly to an assembly of this type whose anchor turns into decking material but does not penetrate the underface thereof.
2. Status of Prior Art It is common practice to cover the roof of a building with a layer of thermal insulation formed of pads or panels of lightweight material such as fiberglass or rigid foam plastic. These panels are laid down on the roof deck and covered by a sheet of polyvinyl chloride, or other water-impermeable membrane to protect the layer against water penetration.
Since the roof is exposed to the elements, it may on occasion be subject to high velocity winds as high as 150 miles per hour. Unless the insulation layer is firmly secured in place, the resultant updraft may blow the layer off the roof. For various reasons such as fire protection, the use of bonding agents to adhere the insulation layer to the deck of the roof is being discontinued, and instead mechanical fasteners are now employed to retain the layer when a strong updraft is encountered. The present practice of securing the insulation layer to the roof deck is by means of load-bearing plates of sheet metal which overlie the insulation layer and are bolted or otherwise mechanically fastened to the deck.
Among the patents which disclose load-bearing or stress plates for this purpose are the Giannuzzi U.S. Pat. No. 4,574,551 the Williams U.S. Pat. No. 1,286,862, the Sandquist U.S. Pat. No. 4,074,501 and the Carlson U.S. Pat. No. 4,288,951.
The concern of the present invention is with an anchor and stress plate assembly usable with two types of decking material. One is relatively soft, such as a porous wood and fiber composite known commercially as Tectum. The other is a hard decking material such as gypsum, plaster board, or low strength cement By "a hard decking material" is meant one which when a hole is drilled therein is capable of being tapped by an auger screw. It is important to note that such hard deck materials are also somewhat brittle and therefore subject to disintegration by an anchor screw unless the screw is of the proper type.
Conventional anchor and stress plate assemblies for these two types of decking materials usually make use of anchors of the toggle type which penetrate the material. Hence when the assembly is installed, the stress plate then engages the upper face of the insulation layer while the toggle then engages the underside of the deck. A serious practical shortcoming of this conventional arrangement is that the toggles are exposed at the underside of the deck and deprive the underside of a clean, finished appearance. When the deck underside forms the ceiling of the building interior, the presence of toggles on this ceiling is unsightly and therefore not commercially acceptable.
Another drawback is that anchors in the form of conventional toggle bolts tend to loosen up as a result of vibratory or other forces, and sometimes in doing so cause debris to fall into the interior of the building. And in loosening up, the anchor may in time fail and result in a blow off of the insulation layer held thereby.
In order to provide an assembly including a nonpenetrating anchor for soft decking materials such as Tectum, the Blucher et al. U.S. Pat. No. 4,642,012 provides an auger-like anchor whose shank is composed of three sections of different diameter, the head of the screw being received in a washer functioning as a stress plate. No means are provided in this assembly to resist loosening of the anchor.
SUMMARY OF INVENTION
In view of the foregoing, the main object of this invention is to provide an improved roof anchor and stress plate assembly of the non-penetrating type for securing a layer of insulation to a deck composed of relatively soft or hard material.
More particularly, an object of this invention is to provide an assembly of the above type in which the anchor, when the assembly is installed, is highly resistant to any force which seeks to turn out the anchor, thereby preventing loosening of the installed assembly.
Also an object of this invention is to provide an assembly whose anchor shank has an auger screw section that functions effectively in both soft and dense decking material.
A significant feature of an anchor in accordance with the invention is that when the auger screw section thereof is turned into soft, relatively low density decking material, this action causes the material to pack into a mass of increased density in the region surrounding the screw, thereby enhancing its holding power; the same auger screw when turned into a hole drilled in hard decking material allowing for easy cutting of a thread in the wall of this hole but with a minimum of crushing or pulverizing of the hard and relatively brittle material.
Yet another object of the invention is to provide an assembly of the above type which may be mass-produced at low cost, and which may be installed without difficulty by a simple torque-producing tool.
Briefly stated, these objects are attained in an anchor and stress plate assembly adapted to secure an insulation layer to the deck of a roof without penetrating the lower surface of the deck which is formed either of relatively soft or hard decking material. The anchor is provided with a flanged head and a shank whose leading section takes the form of an auger screw having a root which tapers toward the tip and a threading about the root whose crests are of approximately uniform diameter. When the anchor is turned into soft decking material, the tapered root of the auger screw then acts to pack this material into a dense mass in the region surrounding the screw to enhance the holding power of the anchor. In hard decking material, a hole must first be drilled therein to receive the auger screw whose root when the anchor is turned in fits within the hole and whose crests then cut a thread in the hole wall to securely retain the anchor.
The stress plate which overlies the insulation layer to prevent uplift thereof has a central depression surrounding an opening defined by a circular series of ratchet teeth. When the anchor is fully turned into the decking material, its head then lies within the plate opening while the flange rests within the depression. The anchor head is provided with a pawl that is deflected by the ratchet teeth when the anchor is being turned in, the pawl engaging the teeth when the anchor seeks to turn out, thereby preventing loosening of the installed assembly.